What is chordate?
In the strategy of categorization, the animate beings land is divided foremost into several majore carnal groups called phyla. There are about 30 carnal phyla presently recognized. The last major group of the carnal land is known as phylum Chordata. It was created by Balfour in 1880. The name of this phylum is derived from two Grecian words, the chorde means a twine or cord, and ata means bearing. Therefore, chordates are animate beings holding a cord, i.e. , notochord. The animate beings belonging to all other phyla of the carnal land are frequently termed ‘the non-chordates ‘ or ‘the invertebrates ‘ since they have no notochord or anchor in their organic structure construction.
Diverseness of chordates:
The chordates show an amazing diverseness of signifier, physiology and home ground.
Numeric strength: The figure of chordate species is non remarkably big. About 49,000 species are on record which are merely half of the life species of molluscs, and less than 1/10 those of arthropods. The two subphyla Urochordata and cephalochordate claim for about 2,500 species. The subphylum Vertebrata includes 46,500 species of these ; fishes are the most legion with an about 25,000 species. It is normally assumed that amphibious species figure about 2,500, reptiles 6,000, birds 9,000 and mammals 4,500.
Size: Despite their modest figure of species, the chordates make a disproportional part to the biomass of the Earth. About all of them are average to big in size. The craniates, in peculiar, are well big and many of them are among the largest of life animate beings. The mammoth bluish giant ( Balaenoptera muscle ) and the smallest fish Philippine gudgeon ( Pandaka ) .
Ecology: The chordates are non merely the largest animate beings in being today, but ecologically they are among the most successful in the carnal land. They are able to busy most sorts of home grounds and they have adapted themselves to more manners of being than any other group, including the arthropods. They are found in the sea, in fresh H2O, in the air, and on all parts of land from the poles to the equator. Birds and mammals have been able to perforate cold clime because they have a changeless organic structure temperature, something no other animate beings have.
Three cardinal chordate characters:
Dorsal hollow nerve cord
The cardinal nervous system of the chordates is present dorsally in the organic structure. It is in the signifier of a longitudinal, hollow or cannular nervus cord lying merely above the notochord and widening lengthwise in the organic structure. The nervus cord or nervous tubing is derived from the dorsal ectodermic nervous home base of the embryo and encloses a pit or canal called neurocoel. There are no distinguishable ganglionic expansions. The nervus cord serves for the integrating and coordination of the organic structure activities.
Notochord or chorda dorsalis
The notochord is an extended rod-like flexible construction widening the length of the organic structure. It is present instantly beneath the nervus cord and merely above the digestive canal. It originates from the endodermal roof of the embryologic archenteron. Structurally, it is composed of big vacuolated notochordal cells incorporating a gelatinlike matrix and surrounded by an outer hempen and an interior elastic sheath.
Pharyngeal gill slits
In all the chordates, at some phase of their life history, a series of mated sidelong gill clefts or gill slits perforate through the guttural wall of the intestine behind the oral cavity. These are diversely termed as guttural, branchial and splanchnic clefts or pouches. They serve chiefly for the transition of H2O from the throat to outside, therefore bathing the gills for respiration. The H2O current secondarily AIDSs in inter eating by retaining nutrient atoms in the throat.
The three common chordates characters were likely features of the hereditary chordates. They distinguish chordates from all other animate beings and appear their common lineage.
Fictional characters common to chordates and higher non-chordates:
There are a figure of characteristics in which the chordates resemble the higher nonchordates or invertebrates.
AXIATION: The organic structure in both has a distinguishable polar axis. The anterior terminal differentiated into a cephalic part or caput that normally proceeds in motive power. The opposite posterior terminal forms a tail in most instances. This longitudinal axis of the organic structure running from caput to tail is known as the antero-posterior axis.
Bilateral SYMMETRY: Due to existence of longitudinal antero-posterior axis, the organic structure of all chordates and most higher nonchordates exhibits bilateral symmetricalness i.e. ; the right and left sides of the organic structure are the exact mirror image of each other.
Celom: A secondary organic structure pit or true celom exists between the organic structure wall and the digestive tubing, and it is lined on all sides by mesoblast. However, it differs in its manner of beginning in different groups of chordates and nonchordates.
TRIPLOBLASTIC CONDITIONS: Invertebrates above the degree of cnidarians and all chordates are triploblastic animate beings. They have three germ beds: – exoderm, entoderm, & A ; mesoblasts.
METAMERISM: Metamerism is a status in which the organic structure is composed of a additive series of similar organic structure sections, called somites or metameres. It is found in three phyla: Annelida, Arthropoda and Chordata. In Annelid and Arthropoda, segmental cleavage is both internal every bit good as external, whereas in chordates it is less clear external.
ORGAN SYSTEMS: In an organsystem, several variety meats work together for the same map, such as digestion, circulation, respiration, etc. It is shown by all chordates and all the non chordates from nemetean worms onwards. However, the craniates show a greater phase of development and cardinal integrity in this than even highest invertebrates.
Promotion of Chordata over other phyla:
Phylum chordate have some advantages over other phyla due to certain characters.
Populating endoskeleton: with the exclusion of echinoderms and a few others, merely chordates possess a living endoskeleton. It grows in size with the remainder of the organic structure so that there is no irresistible impulse to cast it sporadically to let for growing like the non populating chitinous exoskeleton of the nonbchordates phyla. Further, this populating endoskeleton permits greater freedom of motion and indefinite growing so that many chordates are the largest animals of carnal universe.
Efficient respiration: the gills in aquatic chordates and the lungs in tellurian signifiers form efficient variety meats of respiration. The tracheal system of certain arthropods is besides efficient but is suited to animate beings of little size merely.
Efficient circulation: the circulatory system of chordates is good developed and the blood flows freely in the respiratory organs guaranting rapid exchange of gases. Furthermore, the blood-vasular system forms an of import medium for several other critical activities of the organic structure.
Centralized nervous system: the invertebrate phyla show a turning inclination of centralisation of nervous system, making its apogee in the higher chordates. The centripetal systems explains the great power of the chordates for accommodating themselves most successfully to a assortment of environments.
Beginning and lineage of chordate:
While a great trade is known about modern chordates, including the lower signifiers, their beginning remains vague. Scientists have non succeeded in finding which lower signifiers have given rise to them. Their early ascendants most likely were soft-bodied and left no definite fossils remains. They must hold originated prior to Welsh period as the oldest dodos of known craniates have been discovered in late Welsh strata. Most scientists consider that the chordates have originated from invertebrates. Several theories attempt to explicate the beginning of chordates from nonchordate groups, but they have serious drawbacks and are far from being satisfactory. One theory advocates the descent of Chordata from the Echinodermata as such. The singular similarities between the echinoderm and hemichordate larvae are taken as good grounds for common lineage. Garstang suggested that likely unattached auricularian larvae of some hereditary echinoderms evolved in to chordates through paedogenesis, i.e. , protraction of larval life without undergoing metabolism and reproducing sexually. Most animal scientists now favor the deuterostome line of chordate development, harmonizing to which the phyla Ehinodermata, hemichordate, & A ; chordate show common lineage on embryological and biochemical groundss. The protochordates provide the linking nexus between early chordate ascendants and craniates. The distinction likely occurred much earlier than Welsh period. The earliest hints of craniates have been found in the stones of late Welsh and Ordovician. A no. of fishes followed in Silurian and became abundant in the Devonian. The subsequent periods show the development of amphibious vehicles, reptilians, birds, & A ; mammals.
General characters of phylum chordates:
Aquatic, aerial, or tellurian. All nonparasitic with no to the full parasitic signifiers.
Body little to big, bilaterally symmetrical and metamerically segmented.
A postanal tail normally undertakings beyond the anus at some phase and may or may non prevail in the grownup.
Exoskeleton frequently present ; good developed in most craniates.
Body wall triploblastic with three originative beds: exoderm, mesoblast, & A ; entoderm.
Coelomate animate beings holding a true celom, enterocoelic schizocoelic in beginning.
A skeletal rod, the notochord, nowadays at some phase in life rhythm.
A cartilaginous or bony, populating & As ; jointed endoskeleton nowadays in the bulk of members.
Pharyngeal gill slits nowadays at some phase ; may or may non be functional.
Digestive system complete with digestive secretory organs.
Blood vascular system closed. Heart ventral with dorsal and ventral blood vass. Hepatic portal system good developed.
Excretory system consisting proto-or meso-or meta-nephric kidneys.
Nerve cord dorsal and tubular. Anterior and normally enlarged to organize encephalon.
Sexual activities separate with rare exclusions.
Comparison of chordates with nonchordates:
S.NO.
Features
Chordata
NONCHORDATA
1.
Symmetry
Bilateral
Radial, biradial, bilateral or missing
2.
Metamerism
True Metamerism
True or pseudo Metamerism or missing
3.
Post-anal tail
Normally present
missing
4.
Grade of organisation
Organ-system
Protoplasmic to organ-system
5.
Germ beds
Triploblastic
Diploblastic or Triploblastic or absent
6.
Celom
Truly Coelomate
Acoelomate, pseudocoelomate or genuinely coelomate
7.
Limb derivation
From several sections
From same section
8.
Notochord
Present at some phase or replaced by a anchor made of pealing like vertebrae
Notochord or anchor lacking
9.
Gut place
Ventral to steel cord
Dorsal to steel cord
10.
Pharyngeal gill-slits
Present at some phase of life
Absent
11.
Anus
Differentiated and opens before the last section
Opens on the last section or absent
12.
Blood vascular system
Closed
Open, closed or absent
13.
Heart
Ventrally placed
Dorsal, sidelong or absent
14.
Dorsal blood vass
Blood flows posteriorly
Blood flows anteriorly
15.
Hepatic portal system
nowadays
Absent
16.
Hemoglobin
In ruddy atoms
In plasma or absent
17.
Respiration
Through gills or lungs
Through organic structure surface, gills or windpipe
18.
Nervous system
Hollow
Solid
19.
Brain
Dorsal to pharynx in caput
Above throat or absent
20.
Nerve cord
Single, dorsal, without ganglia
Double, ventral, normally bearing ganglia
21.
Rootss of segmental nervousnesss
Dorsal and ventral offprint
Dorsal and ventral roots non divide
22.
Reproduction
Sexual reproduction predominant
Asexual reproduction predominant
23.
Regeneration power
Normally hapless
Normally good
24.
Body temperature
Cold or warm-blooded
Cold
Major subdivisions of phylum Chordatas:
Brief categorization of chordate with characters:
The chordates form a big heterogenous grouping of members differing widely from one another in many respects. This creates jobs in their systematic categorization. Different strategies have been proposed by a figure of taxonomers from clip to clip. The one followed in this is a synthesis of the most recent 1s adopted here for the interest simpleness and proper apprehension
Phylum chordate can be divided in to two groups ; Acrania and Craniata holding contrasting characters.
Group 1 ACRANIA ( protochordata )
All Marine, little, crude or lower chordates. Missing a caput, a skull or braincase, vertebral column, jaws and encephalon. About 2000 species. The Acrania is divided in to three bombers phyla: hemichordate, Urochordata, and cephalochordate chiefly on the place of notochord.
Subphylum 1: HEMICHORDATA
Body divided in to three parts: proboscis, neckband and bole. Notochord doubtful, short, confined to proboscis and not homologous with that of chordates.
Class 1: Enteropneusta Body big and worm-like. Gill-slits legion. Intestine heterosexual. Acorn or lingua worms. 3 households, 15 genera and 70 species. Balanoglossus, saccoglossus.
Class 2: Pterobranchia Body little and compact. Gill slits one brace or none, intestine U-shaped. Pterobranchs includes 2 orders, 3 genera and 20 species. Cepalodiscus, rhabdopleura.
Class 3 Planctosphaeroidea Transparent, unit of ammunition and specialised tornaria larva, holding extensively branched ciliary sets and L-shaped alimental canal, represents this category. Planctosphaera pelagica.
Class 4: Graptolita The dodos graptolites were abundant in Ordovician and Silurian periods and frequently placed as an nonextant category under hemichordate. Their cannular chitinous skeleton and colonial wonts show an affinity with Rhabdopleura. Dendrograptus.
Subphylum 2: Urochordata or Urochordata
Notochord and nervus cord merely in tadpole-like larva. Adult sac-like, frequently sessile and encased in a protective adventitia. Tunicates.
Class 1: Ascidiacea Sessile tunicates with scattered musculuss in adventitia. Solitary, colonial or compound. Gill-clefts legion. Ascidians or sea pip-squeaks. 2 subclass, 3 orders, 12 households, 37 genera and 1200 species. Herdmania, Ciona, Molgula.
Class 2: Thaliacea Free-swimming or oceanic urochordates with round musculuss in adventitia. Sometimes colonial. Salps or concatenation urochordates. 3 orders, 5 households, 9 genera and 30 species. Salpa, Doliolum, Pyrosoma.
Class 3: Larvacea of Appendicularia Tiny, transparent, free-floating. Adults retain many larval characteristics including tail. Merely two gill-slits. 2 orders, 2 families,5 genera and 30 species. Oikopleura.
Subphylum 3: Cephalochordata
Notochord and nervus cord nowadays throughout life along full length of organic structure.
Class leptocardii Body fish like, segmented with distinguishable myotomes and legion gill-slits. Free-swimming and burrowing. Lancelets. One category, one household, 2 genera and 30 species. Branchiostoma, Asymmetron.
Group 2 CRANIATA ( Euchordata )
Aquatic or tellurian, normally large-sized, higher chordates or craniates with distinguishable caput, a vertebral column, jaws and encephalon protected by a skull or braincase. The Craniata includes a individual subphylum, the Vertebrata.
Subphylum 4: Vertebrata
Notochord supplemented or replaced by a vertebral column or anchor composed of overlapping vertebrae. Body divisible into caput, cervix, bole and tail. Normally dioecian. This subphylum is divided into two divisions:
Division 1: Agnatha
Jawless crude fish like craniates without true jaws and paired limbs.
Class 1: Ostracodermi Several nonextant orders of ancient crude to a great extent armoured, palaeozoic, universe ‘s first craniates, jointly called the ostracoderms. Cephalaspis, Drepanaspis.
Class 2: Cyclostomata Body eel-shaped, without graduated tables, jaws and sidelong fives. Mouth rounded and suctorial. Gills 5-16 braces. Parasites and scavengers. 45 species. Lampreys ( Petromyzon ) and hag fishes ( Myxine ) .
Division 2: Gnathostomata
Jawed craniates holding true jaws and paired limbs. For convenience, some taxonomers farther divided Gnathostomatas into two superclasses. All the fishes and fish like aquatic gnathostomes are placed in the superclass Pisces, whereas all the quadrupedal tellurian gnathostomes in the superclass Tetrapoda. Their contrasting characteristics are as follows:
Superclass 1: Pisces
Fishs or fish-like aquatic signifiers with paired every bit good as average fives, gills and scaly tegument
Class 1: Placodermi Several nonextant orders of crude earliest jawed fishes of palaeozoic with cadaverous caput shield movably articulated with trunk shield. Placoderms, Climatius, Dinichthys.
Class 2: Chondrichthyes Mostly marine. Cartilaginous endoskeleton. Skin with platelike graduated tables. Gill-slits non covered by operculum. Pelvic claspers in male. Cartilaginous fishes. Approximately 600 species. Scolidion ( dog fish ) , Chimaera ( rat fish )
Class 3: Osteichthyes Freshwater and Marine. Endoskeleton largely bony.skin holding assorted types of graduated tables other than platelike. Gill-slits covered byan operculum. Males without claspers. 20,000 species. Labeo ( rohu ) , Protopterus ( lung fish ) , Hippocampus ( sea Equus caballus ) .
Superclass 2: Tetrapoda
land craniates with two braces of pentadactyle limbs, cornified tegument and lungs.
Class 1: Amphibia Larval phase normally aquatic and breaths by gills. Adult typically tellurian and respires by lungs. Skin moist, glandular and with no external graduated tables. Heart 3-chambered. Approximately 2500 species. Rana ( toad ) , Bufo ( frog ) , Ambystoma ( salamander ) .
Class 2: Reptilia Terrestrial tetrapods, skin prohibitionist, covered by ectodermic horny graduated tables or bony home bases. Heart incompletely 4-chambered, Cold, respiration by lungs, 7000 species. Hemidactylus ( palisade lizard ) , Uromastix ( spiny-tailed lizard ) , Naja ( cobra ) , Sphenodon, Crocodilus.
Class 3: Aves Typically winging craniates covered with plumes. Fore limbs modified in to wings. No dentition in beak. Heart 4-chambered. Warm blooded. About 9000 species. Struthio ( African ostrich ) , Columba ( pigeon ) , Gallus ( poultry ) .
Class 4: Mammalia Body covered by hair. Skin glandular. Female with mammary secretory organs which secrete milk for suckling the immature. Heart 4-chambered. Warm blooded. Air take a breathing craniates. 4500 species. Echidna ( spinous pangolin ) , Macropus ( kangaroo ) , Rattus ( rat ) , Homo ( adult male ) .
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Books referred:
Chordate fauna by E.L.Jordan and P.S.Verma
Modern text edition of fauna, craniates ( carnal diversity-2 ) by R.L.Kotpal
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